The stimulus payment is based on your 2020 tax status. The IRS just used the 2018 and 2019 returns as a guide. So there are some people such as yourself who received the stimulus that just flat out didn't qualify for it.
Keep the money "for now". When you complete your 2020 taxes, if you are claimed as a dependent on any one else's tax return, and you indicate that on your tax return, you "may or may not" be required to return that money (with no penalties) upon filing your 2020 tax return. So for now, don't spend that money if you haven't already, and expect to have to repay it with your 2020 tax return.
As it stands right now, the IRS says that those who were overpaid will not have to pay back the over payment amount. But there as been no clarity provided as of yet for cases where stimulus money was paid to a recipient that didn't qualify for it.
